Answer
choice $(B)$
Work Step by Step
Equation form:
$\displaystyle \quad f(x)=\frac{N}{1+Ab^{-x}}$,
where $N$ = limiting value.
Reading the graph, we have:
$N=9,$ choice (A) is eliminated.
Initial value is 2, so:
$f(0)=2\Rightarrow\left\{\begin{array}{ll}
2 & =\frac{9}{1+Ab^{0}}\\
1+A & =9/2\\
A & =4.5-1=3.5
\end{array}\right.\qquad\Rightarrow\qquad $choice $(B)$
